How Buffers Affect Your Tone

The buffer vs. true bypass argument still goes on, with both sides being blamed for "tone sucking". The model that most people use is guitar output impedance -> cable capacitance -> amp input impedance. In reality, things are more complicated than that and there are many little variables that can alter tone.
The truth is, there is a difference between plugging directly into an amp, or a true bypass effect chain, and plugging into a buffered effect chain. Let's use a more complex model and take a look at the differences.

The upper schematic shows a simulated humbucking pickup with tone and volume controls and cable capacitance going into a simulated amp's front end. The amp section consists of an the resistors from a tube amp's front end and a capacitor* that simulates the capacitance to ground caused by the tube's grid to cathode capacitance. The lower schematic is the same thing but with a buffer after the cable.

This is how the frequency response turns out:

The direct/true bypass signal chain shows a small increase around 2kHz and a large reduction around and above 3kHz compared to the buffered chain. Which one is better is a personal choice.